Backlash free rotationally adjustable mount in the nature of a transmission

ABSTRACT

A mount according to this invention includes a base and a rotor rotatably mounted to the base. The mount has a central axis. The rotor has an axis of rotation which is coincident with the central axis. A base race is fixed to the base, and a rotor race is fixed to the rotor. A base track face is formed on the base race, and a rotor track face is formed on the rotor race, antipodally spaced from one another. A plurality of bearing balls are held between these track faces. The track faces are frustums of cones so as to make a point contact with the balls.

FIELD OF THE INVENTION

A rotationally adjustable mount which is free from backlash, and whichenables both gross and fine rotational adjustments to be made to arotor, and which is also adaptable to use as a power transmission.

BACKGROUND OF THE INVENTION

It is conventional practice to mount instruments, optical devices, ormanufactured parts on a rotatable table, and to provide means adjustablyto rotate them for inspection or alignment. The objective of thesemounts is to enable the device to be rotated around an axis and placedin a selected rotary position.

Such mounts nearly universally involve backlash, which is slack in thesystem, such that there is a delay in reversal of the mount when theadjustment means is reversed. This is at least an annoyance. It isdesirable that the adjustment means and the mount be very closelycoupled so the operator can quickly and reliably return to a positionwhich he may inadvertently have passed without having to take up systemslack.

Also, it is desirable for the mount to be able to be grossly rotatedquickly, and then to be finely adjusted.

This apparatus is also useful as a power transmission

It is an object of this invention to provide the above features andadvantages.

BRIEF DESCRIPTION OF THE INVENTION

A mount according to this invention includes a base and a rotorrotatably mounted to the base. The mount has a central axis. The rotorhas an axis of rotation which is coincident with the central axis. Abase race is fixed to the base, and a rotor race is fixed to the rotor.A base track face is formed on the base race, and a rotor track face isformed on the rotor race, antipodally spaced from one another. Aplurality of bearing balls are held between these track faces. The trackfaces are frustums of cones so as to make a point contact with theballs.

A drive ring surrounds the balls and traps them against the track faces.The drive ring forms two track faces antipodally spaced from oneanother. They are also frustums of cones, so as to make a point contactwith the balls.

All of the track faces are surfaces of revolution centered on the samecentral axis. All of the track faces make a conical angle with a planenormal to the central axis. Each angle has a numerical value. The anglesmay be different in algebraic sign, which is unimportant to thisinvention. What is important is that each of the faces faces toward theballs, and between them they trap the balls so as to function as a ballbearing.

At least two of the faces make a numerically equal conical angle withthe equator of the ball when it is contacted by all of the track faces.Of the other two, one is not equal to the other. The other angle may beequal to, or different from, the first two when the latitudes of contactare equal relative to the central axis. If they are equal, then theequator of the balls will coincide with a plane normal to the centralaxis. If the contact points are shifted around the ball, then theequator of the ball will also shift.

Rotation of the drive ring drives the balls around the central axis. Byway of explanation, assume what is not the situation--that all fourconical angles were equal. Then the drive ring would drive the ballsaround the tracks on the base and on the rotor, and there would be norelative rotation between the base and the rotor. This would merely be aconventional ball bearing, mounting the drive ring for free rotationaround the base-rotor combination.

Instead, when the angle of one of the faces differs and at least two areidentical, a very different situation arises. Then the two like facesassume a driving relationship on the balls, one or the other of theother two balls will rotate relative to its contact face at a differentvelocity. Then, assuming a sufficient frictional contact such that theball at the contact point and the face at the tangent point move at thesame velocity, then the element which underlies its face will move at adifferent rotational velocity around the central axis. As a result, therotor will rotate relative to the base. The relative rate of rotation isdependent on the relative conical angles.

With this construction, proportional incremental movements can be madewith much larger movements of the outer surface of the drive ring.

The track faces make a frictional contact with the balls which can beovercome by sufficient gross torque on the rotor. Accordingly, should aquick and large rotation be desired, one need only take hold of therotor and turn it. There will be a skidding movement between the ballsand some or all of the track faces, but because the balls and the facesare all hardened surfaces, this will do no harm. After the grossmovement, the drive ring can be used to make a finer adjustment.

This action would not be possible with a geared arrangement. Also notethat a gear arrangement involves backlash, which is entirely absent inthis device.

The described rotation of the rotor occurs as the consequence ofrotation of the drive ring. Accordingly, this mount functions as atransmission, being driven by the drive ring. While the principal use isexpected to be as an adjustable mount and powered by the hand, it ispossible to connect the drive ring to a power source, such as throughgears, belts or chains to a drive shaft. Then a very high ratiotransmission is provided.

Also, the drive ring may be internal rather than external, to enable thedevice to be placed in line with its power source.

The above and other features of this invention will be fully understoodfrom the following detailed description and the accompanying drawings inwhich:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of the invention;

FIG. 2 is a left hand side view of FIG. 1;

FIG. 3 is a cross section taken at line 3--3 in FIG. 1; and

FIG. 4 is an enlarged vignette view of a portion of FIG. 3, showing thegeometry of the invention;

FIG. 5 is a cross-section taken at line 5--5 in FIG. 3;

FIG. 6 is an axial cross-section of the apparatus adapted for powertransmission; and

FIG. 7 is an axial cross-section of another embodiment of the apparatusadapted for power transmission.

DETAILED DESCRIPTION OF THE INVENTION

A mount 10 according to the invention is shown in FIG. 1. It has acentral axis 11 of rotation. A base 12 can be placed on any suitablesupport such as a table. A mounting flange 13 is provided for thispurpose.

A tapered roller bearing 15 rotationally supports a rotor 16 to thebase. It is held to the inner race 17 of the bearing by a retainer bolt18 whose head 19 is above the level of the bottom of the base. A device(not shown) whose rotational position around the central axis is to beadjusted will be mounted by any suitable means to the top surface of therotor. The rotor is freely rotatable around the axis, and as will laterbe shown, if sufficient torque is exerted, a gross adjustment canquickly be made by turning the rotor.

However, this does not accomplish the fine adjustment of position whichit is the principal objective of this invention to provide when it isused as a mount. For this purpose a rotational adjustment means 20 isprovided. The adjustment means includes a second bearing 25. Thisbearing necessarily is a ball bearing. The outer race 26 of the rollerbearing is fixed to the base, and constitutes a fixed base race for theball bearing, with a fixed base track face 27, which is the frustum of acone. Balls 28 of bearing 25 will make point contact with track face 27.

A rotor race 30 is disposed above the base race. It has a rotor trackface 31, which also is the frustum of a cone. Race 30 is slidably fittedon shaft 32 of the rotor, and is biased downwardly by resilient means 33such as a Belleville washer or a wave spring. It bears between the rotorand the rotor race to bias track face 31 against the balls.

Optional splines or any other rotary couplings that is axially resilientmay be provided, for example splines keyed into slots on shaft 32 if itis desired that the rotor race must rotate with the rotor. This is not anecessary element, but does have an advantage to be discussed below.

A drive ring 35 surrounds and completes bearing 25. It includes twodrive track faces 36,37, both frustums of cones, both contacting theballs, but on opposite sides of the equator of the balls.

A more detailed description of the relationships between the tracks willnow be given. Assume that each of these four tracks made the samenumerical angle with the equator 40 of the balls. Of course they differin the algebraic sign of the angle (positive upwardly and negativedownwardly). When they are equal, the drive ring would simply run aroundthe balls, the balls would be rotated by the drive ring, and run aroundthe inside faces along equal antipodal latitudes. Nothing would happenbetween the base and the rotor. This invention specifically excludesthis useless embodiment.

In the actual embodiment, at least one of the conical angles isdifferent from all of the others, and at least a pair should be equal.In the example shown, face 31 has a lesser numerical angle than face 27.Because all of the balls make a point contact with their respectiverace, their paths will be a circular line at the given latitude. Thelatitude of the contact of face 31 is numerically larger than that offace 27, so that its perimeter is also smaller. Reverse direction actionis obtained when the angle is greater.

Now, with the conical angles at the drive track faces equal, and atleast one of the paths at the other faces is different, something mustyield. In this device it is the rotor race, which will rotate relativeto the base race, taking the rotor with it. The drive ring can be madecomparatively large, so that it is capable of making very small angularadjustments of the rotor.

The bias means can generally be relied on to keep the rotor from turningrelative to the rotor race. However, if desired, the splines can beprovided to assure it. Surprisingly this does not necessarily create abacklash because a sufficiently strong spring will generally keep themtogether, except in very strenuous operation, which usually does notoccur, and they are closely fitted.

If a gross movement is desired, the rotor will be turned without turningthe drive ring. Then the balls will simply drag along at least one ofthe tracks. However, the tracks and the balls are very hard, and thiswill not adversely affect them, especially if the bearing is lubricated.

Suitable angles for the track faces, given in absolute degrees are asfollows:

Drive tracks 36 and 37, 45°

Base track face 27, 45°

Rotor track face 36, 39°. This provides approximately a 20:1 rotationbetween the rotor and the drive ring.

Further with regard to the relationship between the track faces, itshould be observed that the equator of the balls can lie in a planewhich is not normal to the central axis of the mount. The polar axis ofthe balls is determined by the relative angles between the two trackfaces which are on the same structure, in this case the drive ring. Ifthese angles are numerically equal, then the polar axis is parallel tothe central axis. However, if they are different, the polar axis aroundwhich the balls rotate will be tilted relative to the central axis. Thenthe equality of the angles refers only to the equator of the balls inmotion. This arrangement functions identically with the illustratedexample.

The embodiment of FIG. 1 can be used as a power transmission by couplingit to power means (not shown) with gears or belts, when in-linetransmission is not required.

If in-line transmission is desired, the embodiments of FIGS. 6 and 7 maybe used instead. FIG. 6 also illustrates the fact that the drive ringcan be internal as well as external.

Transmission 60 in FIG. 6 is symmetrical around a central axis 61.Shafts 62, 63 are provided for input and output of power. Both may beused for either purpose, depending on the ratio desired.

Shaft 62 is integral with an internal drive ring 64 which bears twotrack faces 65, 66.

Race 67 bears a track face 68. Race 69 is integral with shaft 63, andbears a track face 70. One of the races will be fixed ("grounded") tochassis (not shown). Then the other of the races will be rotatablerelative to it. Either race may be "grounded".

Appropriate bearings are provided as illustrated.

FIG. 7 shows a variation of a transmission 75, in which drive ring 76 isexternal rather than internal, and it is not necessarily used to receivepower. The term "drive ring " throughout this specification refers tothe member which bears the two interconnected track faces.

In this embodiment, shaft 78 may receive power, which will betransmitted to shaft 79 (which may be tubular). Again any part can begrounded, with the other two used for input and output.

Track faces 80, 81, 82 and 83 are provided as in the other embodiments.

In the embodiments of FIGS. 6 and 7, the track faces which conform withthose described in FIGS. 1-4, and function identically. Appropriatebearings are provided.

Suitable traction fluids as are present in existing traction drives areplaced around the bearings to assure proper lubrication and traction.Appropriate seals are provided to retain the fluid.

Frusto-conical track faces have been specified as the purest form ofpoint contact. Of course the track faces could be modified to haveconvex regions for the point of contact, or even recessed ring-likeregions. In all of these situations, the relative velocities of theraces and balls are of importance and are intended to be within thedefinitions of conical frustrums.

This invention is not to be limited by the embodiments shown in thedrawings and described in the description which are given by way ofexample and not of limitation, but only in accordance with the scope ofthe accompanying claims.

I claim:
 1. Apparatus in the nature of an adjustable mount or powertransmission, said apparatus having a central axis, and comprising:afirst race and a second race, each said race bearing a track face; adrive ring bearing a pair of track faces; a plurality of bearing ballstrapped between said track faces making a point contact with all of saidtrack faces simultaneously, said first and second races being separatelyrotatable, all of said track faces being surfaces of revolution at thesaid points of contact and at that those points being frusto-conical,each having a numerical angular value to the equator of the balls inmotion, at least two of said values being equal, and at least one beingdifferent from those two; whereby when the drive ring is rotated, thepolar axis of rotation of the balls is determined by the angularrelationships between the track faces on the drive ring, the rate ofrotation of the races relative to one another being determined by theangular difference between the unequal angle and one of the otherangles.
 2. Apparatus according to claim 1 in which one of said first andsecond races is fixed to a base and the other is fixed to a rotor. 3.Apparatus according to claim 2 in which said drive ring is external, itsrespective track faces facing inwardly and toward one another. 4.Apparatus according to claim 3 in which the said two equal angles are inthe drive ring, the unequal angle being on one of the races. 5.Apparatus according to claim 1 in which said drive ring is mounted to ashaft, having its track faces facing outwardly, and in which one of theraces is fixed to a shaft, said shafts being adapted for transmission ofpower.
 6. Apparatus according to claim 5 in which the angles of thetrack faces on the drive ring are numerically equal.
 7. Apparatusaccording to claim 1 in which said drive ring is external to said races,said races being adapted for transmission of power.